CA1105821A - Fibrous material and method of making the same - Google Patents

Abstract

ABSTRACT
High loft, low density, nonwoven fibrous materials and methods of making the same are provided, said material comprising at least two layers of irregularly arranged, intersecting, overlapping, mechanically interengaged fibers, one of the layers including thermoplastic synthetic wood pulp fibers at least in the portion thereof at the interface to the other layer, at least some of the thermoplastic synthetic wood pulp fibers in the one layer being in contact with and fused with segments of fibers of said other layer.
The material is produced by air-laying at least the synthetic wood pulp containing layer, and then applying heat without pressure to fuse and bond at least some of the thermoplastic synthetic wood pulp fibers in said one layer to the remaining fibers in said one layer and to fibers in the other layer.
This application relates to high loft, low density, nonwoven fibrous materials, having synthetic wood pulp fibers located at at least a mid-portion thereof parallel to or including its median plane, and to a method of producing such a material.

Description

3 1~51~}Z~

Background of the Invention:
Synthetic polymeric fibers that have physical and morphological characteristics generally similar to wood pulp ~ibers produced from natural woods have been known for approximately 10 years. Examples of such fibers are the synthetic wood pulp fibers formed of polyethylene that are sold by Crown Zellerbach under the trademark SWP.
Various methods of making synthetic wood pulp fibers are known, including (1) solution polymerization accompanied by stirring, (2) dissolving a preform~d polymer and subjecting the solution to an anti-solvent, or (3) forming the polymer at the interface between ,~

'':'' 1~5~1

-2- JBP 88 liquid layers, with localized stirring provided to pull the polymeric material thus produced into fibrillated forms. Examples of methods of producing synthetic wood pulp fibers are disclosed in U.S. Patent Nos. 2,999,788;
2,708,617; 2,798,283; 3,560,318; 3,081,519, 3,003,912;

3,068,527; and 3,290,207; South African Patent 697,431;
United Kingdom 1,102,342; and Netherlands Patent Appli-cation A132/48-7313178.
As used in this specification and the appended claims, the term "synthetic wood pulp fibers" means synthetic, water dispersible, thermoplastic, elongated, supple, randomly bent, polymeric fibers or fibrils generally similar in size and shape to conventional wood pulp fibers produced from naturally occurring woods.
Each such "synthetic wood pulp fiber" is of irregular cross-sectional.shape measured at any given point along its length, and in addition is non-uniform in cross section along its length. The predominant shape of the fibers is usually rather ribbon-like.
The present invention utilizes synthetic wood pulp fibers in a high loft, low density, nonwoven fibrous materials such as an air-lai.d web or fabric.
Nonwoven materials are structures which consist of an assemblage or web of irregularly arranged fibers, joined randomly or more or less systematically by mechanical, chemical or other means. These materials are well-known in the art, having gained considerable prominence within the last twenty years or so in the consumer market, the industrial commercial market and the hospital field. For example, nonwoven materials are becoming increasingly important in the textile and related fields, one reason being because of their low cost of manufacture for a given coverage as compared to the cost of more conventional textile fabrics made by weaving, knitting or felting. Typical of their use is the production of hospital caps, dental bibs, eye pads, dress shields, 3L1~5~2~

shoe liners, shoulder pads, skirts, hand towels, handker-chiefs, tapes, bags, table napkins, curtains, draperies, diaper facings, underpads, hospital drapes, and the like.
Generally speaking, nonwoven materials are available today in a wide range of fabric weights of from as little as about 100 grains/sq. yd. to as much as about 4,000 grains/sq. yd. or even higher.
A number of processes and types of apparatus are known for producing nonwoven materials. These in-clude (1) mechanical techniques (e.g. carding orgarnetting), (2) wet laying techniques (e.g. inclined wire paper apparatus, cylinder paper apparatus, etc.), and (3) air-laying techniques. The high loft~ low density, nonwoven materials such as webs or fabrics to which this invention relates may suitably be produced, in the manner to be explained in detail below, from layers of material manufactured by well-known air-laying processes.
One product of this invention utilizes synthetic wood pulp fibers in a novel high loft, low density, nonwoven, two-ply fibrous material that is use-ful as one component of an infant's disposable diaper.
The material is also useful in other absorbent products such as sanitary napkins, surgical bandages, disposable bed pads, and the like.
The present invention also utilizes synthetic wood pulp ibers in a high loft, low density nonwoven fibrous material, such as an air-laid web, which is one component of a wipe, swab, or other similar cleaning 3 device. Cleaning devices of this t~pe should possess two characteristics, both of which are important but which are mutually inconsistent. First, the device must have a substantial amount of wet strength in order to hold the desired shape and avoid disintegration of the fibrous material when in use. This characteristic is ,~ best provided by a compactly assembled aggregation of 1~5~

-4- JBP 88 fibers bonded with an adhesive binder. Second, the cleaning device must have a high degree of liquid absorbency, as well as a substantial amount of resiliency in its structure in order to be most efficient in adapt-ing to corners to be cleaned. This characteristic isbest provided by a high loft, low density, nonwoven fibrous material in which the fibers are loosely assembled.
The two contradictory objectives ~ust described can be achieved by joining nonwoven webs of different types to form the desired cleaning device. Thus, a wet-laid nonwoven web of compactly assembled fibers bonded with a water insoluble adhesive binder can be used to provide the necessary wet strength. An air-laid nonwoven web of loosely assembled fibers can be used to provide the high loft, low density, liquid absorbent layer.
Use of such different fibrous layers to form the two-ply cleaning device of this invention presents difficulties in causing the two layers to adhere to each other without destroying the liquid absorbent character of the second layer. These difficulties are surprisingly avoided by the present invention.
S ~ ion In the method of this invention, a first layer of irregularly arranged, intersecting, overlapping, mechanically interengaged fibers is brought together with a second layer of similarly disposed loosely assembled fibers that includes synthetic wood pulp fibers in portions of the layer that are immediately ad~acent the first layer when the two layers are brought together.
3 This brings at least some of the synthetic wood pulp fibers of the second layer into contact with fibers of the first layer. Both layers may include, and the second layer does include a multiplicity of interstices between their respective fibers, at least some of the interstices of the second layer being of a width at ,,:

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, ~5~ JBP 88 least two times as wide as the mean diameter o~ the fibers of the first layer.
In one form of the method of this invention, wherein the fibers of the first layer are also loosely assembled, defining a multiplicity of interstices at least some of which are of a width at least two times as wide as the mean diameter of the synthetic wood pulp fibers of the second layer, the second layer is supported as a base layer, with one of its sur~aces exposed for positioning of other fibers thereon. The second layer may or may not be self-supporting, as desired. In this form of the method, the first layer is positioned upon the exposed surface of the base layer, to bring at least some of the synthetic wood pulp fibers in this second layer into contact with fibers of the first layer. Or, if desired, the second layer contain-ing synthetic wood pulp fibers may be positioned upon the first fibrous layer, either self-supporting or not, as a base layer.
Because of the supple nature of synthetic wood pulp fibers, it would be expected that substantially all such fibers in the second fibrous layer that are position-ed in contact with fibers of the first layer would be matted down against the fibrous first layer. For it would be expected that the contact between fiber segments in the first layer and fiber segments of synthetic wood pulp in the second layer would tend to be of the type in which one fiber segment lies either parallel to or at an angle to another fiber segment on top of that other 3 fiber, with the areas of contact thus being essentially only two-dimensional because confined to the precise interface between the two layers. Consequently, even though it is well-known that synthetic wood pulp fibers are thermoplastic and can serve to bond various layers of material to each other under heat and pressure (as disclosed, for example, in the section headed

5~Zl

-6- JBP 88 "Applications -- ~onwovens and Laminates" in the September 1974 publication by Crown Zellerbach entitled S~IP), with the areas of contact between layers of loosely assembled fibers being only two dimensional it would not be ex-pected that heating the regions on either side of theprecise interface between the two fibrous layers in the absence of pressure would produce an adequate bond be-tween the synthetic wood pulp fibers of the second layer and the fibrous first layer.
Surprisingly, it has been discovered that excellent delamination resistance may be provided in accordance with this invention when the second layer includes synthetic wood pulp ~ibers in a quantity sufficient to occupy at least about 10~ of the area occupied by exposed fiber segments contained in said second layer at its boundary surface, and the t~o fibrous layers in contact with each other are heated in the absence of pressure to produce fusing of the synthetic wood pulp fibers that are present in at least the second layer. With a homogenously blended nonwoven fabric, 40~ or more by weight of thermoplastic fibers is usually required for reliable fusion bonding of one fibrous layer to another. It has been discovered that with the method of this invention, which utilizes synthetic wood pulp fibers, the total quantity of such fibers required for a reliable bond between layers may be as low as lO~
by weight of a homogenously blended layer. Apparently, there is in fact sufficient three-dimensional interfiber contact--which extends beyond or bridges the precise interface between the two layers of the fibrous material and into the two layers themselves--to produce a re-liable bonding, and resulting resistance to delamination, after heat is applied to the synthetic wood pulp fibers lying in the region on each side of that interface.
An easily delaminateable two-ply facing - material is also provided in accordance with this 5~3Zl

-7- JBP 88 invention when the seco~d layer includes no more than 6%
synthetic wood pulp at its boundary surface, and a water soluble binder is also used at the interface to bond the layers. The two-ply facing material of this embodiment comprises a first layer of loosely assembled natural wood pulp fibers and a second layer of similarly disposed fibers including intermixed natural wood pulp fibers and synthetic wood pulp fibers. The synthetic wood pulp fibers in the second layer, are in contact with and heat fused with other fibers in the layer to form a fiber structure of sufficient wet strength and integrity to ` be self-supporting in both dry and wet condition without any additional binder.
Fibers in each o~ the two layers are also bonded with one another and with ~ibers in the other layer by a water soluble adhesive binder to provide the desired mechanical integrity for normal handling of the dry material as a whole. In addition, the bonding of fibers of the first layer to each other by the intro-duction of adhesive binder avoids disintegration of the first layer when the bond between the two layers (1) is first weakened by immersion in the water o~ a flush toilet for a limited time to dissolve out only a portion of the water soluble binder, and (2) is then ruptured by pulling the two layers apart. Following the rupture of the bond between the layers, the first fibrous layer can be deposited in the flush toilet, where the re-mainder of the water soluble adhesive binder will be dissolved out and the first layer will disintegrate into separate, individual fibers and small clumps of ~ibers.
The water soluble adhesive binder employed should be substantially less soluble in body fluids such as urine than in water, and preferably substantially insoluble in such fluids.
35 The present invention also makes possible the prod~ction of high loft, low density, nonwoven 4ibrous J ~5~21

-8- JBP 88 materials having the characteristics o~ high liquid absorption and high liquid retention. The nonwoven fibrous material of this embodiment c~mprises loosely assembled fibers including both natural wood pulp fibers and synthetic wood pulp fibers; these two types of fibers being present in different proportions in at least three different regions or layers positioned parallel to the median plane of the material.
To produce a high level of liquid absorption in the product of this embodiment, it is necessary to have a facing reglon at one external boundary surface of the nonwoven material that is not too water repellent to prevent a quantity o~ aqueous liquid from passing through it into the main body of the material, but has a lesser affinity for water than the interior region of the material, in order that liquid that has passed ~through the facing region from the outside will remain within the material rather than pass back out through the facing region. While providing this desired balance of wettability, the facing region must have an external boundary surface that also exhibits good softness and abrasion resistance.
Still different characteristics are required of the central region of the nonwoven material, as well as the region adjacent the other external boundary - surface of the material, in order to give the product of this embodiment of the invention a high level of liquid retention. Thus, the central portion of the material must constitute a reservoir region in which liquid can be sorted once it has passed through the absorbent facing region. At the same time, the region of the material that defines the external boundary sur-face that lies o~posite the facing region should provide good wet strength, softness and abrasion resistance, as well as provide an effective barrier to the passage of - any substantial amount of aqueous liquid such as would - ' ~

58Zl ~9- JBP 88 defeat the desired property of high liquid retention by the material.
~ urprisingly, it has been found that this balance of certain characteristics, and the contrasting of other characteristics depending upon the location within the nonwoven material of this embodimen~, can be achieved by incorporating different, controlled amounts of natural wood pulp fibers and synthetic wood pulp fibers in the three regions of the material just de-scribed. In the manufacture of the product of this embodiment, the desired proportions of natural and synthetic wood pulp fibers are first positioned in the indicated regions of layers, and the fibrous assemblage is then subjected to heat without pressure to form a stable fibrous structure in which the three different regions exhibit different desired characteristics.
The facing region or first layer comprises synthetic wood pulp in 6~ to 30% by weight of fibers.
The reservoir region or second layer comprises synthetic wood pulp in a smaller proportion than said first layer, and the region which defines the external boundary sur-face tha~ lies opposite the facing region, or third layer, comprises synthetic wood pulp in a proportion greater than the proportion of such fibers in the second layer, but less than that of the first layer.
The method of this embodiment of the invention co~prises bringing together at least three layers of fibers in the proportions described above and applying heat in the absence of pressure to the plurality of 3 fibers making up the various layers, to fuse and bond at least some of the synthetic wood pulp fibers with other fibers to form a self-supporting fiber structure in the absence of any additional binder.
The product of this invention in another embodiment is a wipe, s~ab, sponge or other cleaning device which includes a backing la~er and a liquid $~321 - -absorbent layer attached thereto. The backing layer or first layer is formed of irregularly arranged, inter-secting, overlapping, mechanically interengaged, compactly assembled natural wood pulp fibers bonded to each other with an adhesive binder to provide wet strength. The liquid absorbent layer or second layer is formed of similarly disposed fibers except that they are loosely assembled with a multiplicity of interstices between them and are not necessarily bonded to each other by means of an adhesive binder. The fibers of the second layer include both liquid absorbent natural wood pulp ~ibers and wettable synthetic wood pulp fibers.
In another embodimént, the cleaning device may c~mprise a three-ply material with the first layer sandwiched between two liquid absorbent layers, each of which contains wettable thermoplastic synthetic wood pulp fibers, as described above.
The layers are emboss laminated together, with segments of some of the synthetic wood pulp fibers of the second and third layer being heat fused and bonded to the first layer in a discontinuous pattern of embossed areas, to provide a reliable bond between the two layers.
The embossed areas alternate with unembossed areas across the backing layer. The synthetic wood pulp fibers located in the unembossed areas are heat fused and bonded to each other and to other fibers in the second fibrous layer, to provide a three-dimensional network of stabilized absorbent cellulose fibers which is not subject to collapsing when wet, and which has 3 good liquid holding capacity, in those unembossed por-tions of the second layer.
The bonded ~ibrous first layer of the product of this embodiment is similar to wet strength tissues sold c~mmercially as disposable cleansing and wiping tissues. Such bonded fibrous tissues are not ordinarily - capable o~ being laminated with other fibrous materials J
. . ,. ~`,.

without the use of adhesive binder, or the full-area lamination ~ith synthetic wood pulp fibers disclosed in the section headed 'tApplications -- Nonwo~ens and Laminates" in the September 1974 publication by Crown Zellerbach entitled SWP. Surprisingly, the presence of the synthetic wood pulp fibers in the second, liquid absorbent, layer of the product of this invention pro-duces a reliable bond between the two layers without any such adhesive binder, and with only discontinuous emboss bonding as described. Another surprising result is the fact that the double bonding actions of the emboss lamination and the generalized heating of the synthetic wood pulp fibers of the unembossed areas appear to oper~
ate independently of each other, to render the unembossed areas a three-dimensional fibrous network of stabilized `
absorbent cellulose ~ibers having good liquid holding capacity.
Brief D_scription of the Drawing The invention will now be described with reference to the accompanying drawing, in which:
Figure 1 is a diagrammatic representation of a portion of a first layer of irregularly arranged, loosely assembled fibers that contains no synthetic wood pulp fibers and may be one component of the fibrous material of this in~ention, Figure 2 is an enlarged diagrammatic represen-tation of the fibrous material of Figure l;
Figure 3 is a diagrammatic representation of a portion of another layer of irregularly arranged, loosely assembled fibers, including textile length 3 fibers but no synthetic wood pulp fibers, that may constitute the first layer of the fibrous material of this invention, Figure 4 is an enlarged diagrammatic represen-tation of a portion of a second layer of irregularly : 35 arranged, loosely assembled flbers that is one component ~ S8%~

of the product of this invention, in which synthetic wood pulp fibers are intermingled with natural wood pulp fibers;
Figure 5 is an enlarged diagra~atic represen-tation in cross-section of the first fibrous layer of Figure 3 being brought together in the first step of the method of this invention with a second layer of synthetic wood pulp fibers that is positioned below it;
Figure 6 is a diagrammatic representation in cross-section of the fibrous material formed by bringing together the two fibrous layers of Figure 5;
Figure 7 is an enlarged cross-sectional view of a cleaning device constructed in accordance with this invention;
Figure 8 is an enlarged cross-sectional view of another cleaning device constructed in accordance with this invention;
Figure 9 is an enlarged, fragmentary diagrammat-ic representation in cross-section of a fibrous material having good liquid absorbency and retention, which is constructed in accordance with this invention, Figure 10 is a diagrammatic side elevation view of one form of apparatus for producing a fibrous material of this invention; and Figure 11 is a diagrammatic side elevation view of another form of apparatus for producing another fibrous material of the invention.
Detailed Descri~tion of the_Invention-Figure 1 is a diagrammatic representation of a first layer 20 of irregularly arranged, intersecting~
overlapping, mechanically interengaged, loosely assembled fibers defining interstices therebetween which may com-prise one component of the product of this invention.
The term "mechanically interengaged" is used in this specification and claims to refer to fibers (usually - 35 randomly bent) that are interlocked or interentangled ~SB2~

with other fibers to provide a degree of structural integrity whether or not binder is present in the layer of fibers.
The fibers of fibrous layer 20 may comprise natural fibers such as cotton, flax, silk, wool, wood pulp, ~ute, etc., mineral fibers such as glass; artifi-cial fibers such as viscose rayon, ethyl cellulose or cellulose acetate; synthetic fibers ~uch as polyamides, polyesters, acrylics, vinylidene chloride, poly~inyl-chloride, polyurethane, etc., alone or in combinationwith one another. The melting point or degradation temperature of these fibers must be higher, preferably by as much as 10 to 20C., than the melting point of the synthetic wood pulp fibers contained in the second fibrous layer of the product of this invention. The fibers represented by the drawing of Figure 1 are approximately 1/4 inch to 1/2 inch viscose rayon fibers.
Relatively long textile type fibers above normal papermaking lengths and close to normal textile length~ say of about 3/8 inch to 2 inches or longer, are preferred for some applications. Shorter fibers below 1/4 inch in length and within the papermaking range may be used in other applications. It is preferred, however, that any shorter papermaking fibers employed be unbeaten or substantially unhydrated if a textile-like fibrous material is desired as the end product. Shorter wood fibers may be used to decrease the cost of the product of this invention, with longer fibers intermixed there-with to provide the strength desired-in the resulting product.
F~gure 2 is a diagrammatic representation giving an enlarged view of first fibrous layer 20 of Figure 1, and the fibers shown in the figure are thus again 1/4 inch to 1/2 inch viscose rayon fibers. In Figure 2 the fibers are disposed in the same manner as in the fibrous layer of Figure 1, with the fibers - ~
, .

5 ~ 2 ~

de~ining interstices 32 between adjacent fibers of the layer. Some interstices in fibrous layer 20 are quite s~all, but at least some of the interstices between flbers in the layer, as shown in Figure 2, have a width at least twice as large as the mean diameter of the fibers that ~ake up second fibrous layer 32 to be de-scribed below.
Figure 3 is another diagramm~tic representation of a first fibrous layer 23 for use in the method of this invention. In this fibrous layer, shorter fibers 24, approximately 1/4 inch to 1/2 inch in length, are intermixed with longer fibers 25 (shown as dark fibers in Figure 3) which are about 1 inch to 2 inches in length.
Figure 4 is a diagrammatic representation of a second layer 26 of irregularly arranged, loosely assembled fibers comprising one c~mponent of the product of this invention. In this embodiment, synthetic wood pulp fibers 27 (stippled in the drawing) a~e inter-mingled with natural wood pulp fibers 28.
If desired, fibrous layers 20, 23 and 26 may be formed by means of an air deposition process.
Figure 5 is a diagrar~natic representation of an enlarged cross-sectional view of first fibrous layer 23 of Figure 3, shown being brought together in the first step of the method of this invention with second fibrous layer 32 that is- positioned below it. First fibrous layer 23 contains shorter fibers 24 and longer fibers 25 (stippled in Figure 5) interrningled therewith.
Loosely assembled fibers 24 and 25 of first fibrous layer 23 are irregularly arranged, intersecting, overlapping and mechanically interengaged with each other.
In the embodirnent shown, second fibrous layer 32 is constituted of synthetic wood pulp fibers 34, which are disposed in a similar l-nanner to fibers 24 and 25 of first fibrous layer 23. This includes the fact ~S~Z:l that synthetic ~ood pulp fibers 34 ~orm interstices between individual fiber se~ments some of which inter-stices have a width at least twice as large as the mean diameter of the fibers that make up fibrous layer 23.
Fibers 34 have an average length of about 1/4 inch.
As is seen from Figure 5, the greater part of , the fibrous mass that comprises first fibrous layer 23 lies within the interior of the fibrous structure as a whole. In fact, in the case of a number of the fibers the individual fiber lies within the interior of the fiber structure for the entire fiber length. However, a number of fibers of layer 23 have free fiber ends 36 extending outwardly from at least one boundary surface of the layer.
In Figure 5, a substantial number of free fiber ends -36 extend downwardly f,rom plane 38, which is the effective lower boundary surface of fibrous layer 23 as the layer is being moved into position on second fibrous layer 32 below it. Second fibrous layer 32 likewise 20 has free fiber ends 40 extending outwardly from the layer. In Figure 5, a substantial number of free fiber ends 40 extend upwardly from the plane of upper boundary surface 42 of layer 32.
In the embodiment under discussion, all the fibers 25 34 present at upper boundary surface 42 of second fibrous layer 32 are synthetic wood pulp fibers, and all these ,fibers are mechanically interengaged with other fibers 34 in layer 32. - Excellent reslstance to delamination is obtained when synthetic wood pulp fibers 34 mechanically 30 interengaged with other fibers in second layer 32 are present at boundary surface 42 in a quantity sufficient to occupy at least about 10% of the area occupied by exposed fiber segments of all kinds contained'in layer 32 at the boundary surface in question.
I~ another embodiment of the inventiong synthetic wood pulp fibers are present at the boundary . ' ' :
, surface in a quantity sufficient to occupy no more than 6~ of the area occupied by exposed fiber segments at the boundary surface and a water soluble adhesive binder is present in the first and second layers at least at the inter~ace thereof, creatin~ a bond between the layers of sufficient strength to-avoid damage to the bond between the layers during no-rmal handling in the dry state, but allowing the first layer to be removed from the second layer in the manner referred to above.
In another embodiment of the invention shown in Figure 7, the first layer 12 is comprised of irregular-ly arranged, intersecting, overlapping, mechanically interengaged, compactly assembled natural wood pulp fibers such as a wet-laid nonwoven web. The fibers of first layer 12 are bonded to each other with adhesive binder to provide wet strength, the binder preferably being a hydrophilic binder with no surfactant. First layer 12 is similar in construction to fibrous webs sold com~ercially for use as disposable cleansing and wiping tissues.
A liquid absorbent fibrous layer, the second layer 16. The fibers in second layer 16, the liquid absorbent fibrous layer, includes both liquid absorbent natural wood pulp fibers and wettable synthetic wood pulp fibers, all of which have generally the same morphology and appearance. The fibers are disposed in the same manner as are the fibers of first layer 12, except that they are loosely assembled rather than compacted, resulting in a high loft, low density structure such as an air-laid nonwoven web. Layer 16 does not have an adhesive binder distributed throughout the fibers as does first layer 12.
As indicated in Figure 7, the remaining synthetic wood pulp fibers that are not heat fused and bonded to backing layer 12 are heat fused and bonded to each other and to other fibers in second layer 16 in - . , .

.

.

-~5821 regions 20 of that layer lying between embossed areas 14.
A three-dimensional network of stabilized absorbent cellulose fibers which is not subject to collapsing when wet and has good liquid holding capacity is thus provided in unembossed areas 20 of second fibrous layer 16.
Fig~re 8 shows a three-ply cleaning device with two liquid absorbent layers, the second and third layers, reinforced by a single first layer 112. The second and third layers, 116A and 116B respectively, are similar to absorbent layer 16 described above with unembossed area 120A in layer 116A and unembossed areas 120B in layer 116B similar to unembossed areas 20 in layer 16 described above. Embossed areas-114 provide the bonding o~ the layers to each other.
The product of another embodiment of this in-vention illustrated in Figure 9, is a high lo~t, low density, nonwoven fibrous material having good wet strength, softness, abrasion resistance, and liquid absorbency and retention. The material-comprises a plurality of irregularly arranged, intersecting, over-lapping, mechanically interengaged, loosely assembled fibers including both natural wood pulp fibers and synthetic wood pulp fibers. The two types of fibers are present in different proportions in various regions or layers positioned parallel to the median plane of the material.
As indicated in Figure 9, nonwoven ~ibrous material 10 is comprised of fibers arranged as described above in first layer or facing region 12, second layer 3 or absorbent reservoir region 14, and third layer or capillary distribution network region 16. Regions 12 and 16 are contiguous with region 14 and lie on opposite sides thereof.
With synthetic wood pulp fibers distributed throughout all three layers of the absorbent fibrous ~aterial of this invention, a plurality of contacts of ' 1~!5~21 -18- JBP 8~
synthetic wood pulp fibers with each other and with the other fibers of the material are present from one exter-nal surface of the material to the other. At at least some of these contact points, segments of synthetic wood pulp fibers are heat fused with other segments of syn-thetic wood pulp fibers or with segments of other fibers, to form a self-supporting fibrous structure in the absence of any additional binder.
The desired characteristics of first layer 12 are obtained when synthztic wood pulp fibers are present in an amount from about 6~ to about 30~ by weight of all the fibers present in the layer.
The wet strength and abrasion resistance of absorbent fibrous material 10 are improved if exposed boundary surface portions 18 of first layer 12 contain about 20% to about 30~ by weight of synthetic wood pulp fibers. In such case, the remainder of layer 12 may contain about 6~ to about 30~ by weight of synthetic wood pulp fibers.
Second layer, or absorbent reservoir region 14, like first facing region 12, includes both natural wood pulp fibers and synthetic wood pulp fibers. Or-dinarily, no other types of fibers are included in this region. Segments of synthetic wood pulp fibers are heat fused with other segments of synthetic wood pulp fibers and with segments of natural wood pulp fibers, to form a self-supporting fibrous structure in the absence of any additional binder.
Synthetic wood pulp fibers are present in 3 second layer 14 ln a smaller proportion than the pro-portion of synthetic wood pulp fibers in first layer 12.
Third layer 16 of fibrous ~aterial 10, which provides a capillary distribution network, contains both natural wood pulp fibers and synthetic wood pulp fibers, and usually no other types of fibers. Synthetic wood . pulp fibers are present in this layer in a proportion ... . .
"
., . ~ . ~ : :.
, 1~S~32~

greater than the proportion of synthetic wood pulp fibers in second layer 14, but less than the proportion in first layer 12.
~ith respect to Figure 9, it should be pointed out that while ~or purposes of clarity this figure shows fibrous layers 12 through 20 adjoining each other at sharply defined interfaces, this is only a diagrammatic showing. In the actual product of this invention there is a more or less gradual transition from o~e fibrous layer or region to another, with fibers intermingled with each other while each layer or region merges into the ad-~oining one.
In the first step of one method of this inven-tion, first layer 23 and second layer 32 are brought together as illustrated, for example, in Figure 5. In the embodiment shown, second layer 32 consisting of synthetic wood pulp fibers 34 is supported as a base layer for positioning the fibers of first layer 23 there-upon. First layer Z3 is positioned upon base layer 32, as illustrated in Figures 5 and 6, in the form of a self-supporting web of fibers, which may be already bonded, or unbonded, as desired.
If desired, first layer 23 shown in Figure 3 may be deposited upon second layer 32 by forming layer 23, by means of an air deposition process and simul-taneously positioning it upon layer 32 as a base layer.
The left-hand portion of Figure 10 provides a diagrammat-ic showing in side elevation of apparatus for this form of the method of this invention, similar to the web forming apparatus disclosed in ~ommonly assigned~Patent Nos. 3,740,797 to Farrington, 3,768,118 to Ruffo et al, and 3,772,739 to Lovgren.
In Figure 10, second layer 32 is fed from supply roll 50 onto the upper reach of endless belt 52, which is moving fr~m left to right as shown. At the same time, first layer 23, such as shown in Figure 3, is iL1~5~21 simultaneously formed and deposited upon second layer 32, to move from left to rig~t with layer 32 while interfiber contact such as described below in some detail in connec-tion with Figure 6 is produced.
Natural wood pulp fibers 24 and textile length fibers 25 (Figure 3) are deposited by air deposition apparatus 54 on second fibrous layer 32 to form first layer 23. Wood pulp board 56 is fed into apparatus 54 between guide plate 57 and feed roll 58, into edgewise contact with lickerin 60, which breaks the board up into individual natural wood pulp fibers. At the same time, a supply of textile length fibers in the form of carded web 61 is fed between guide plate 62 and feed roll 63 into lickerin 6~, and from there-the ~ibers are directed onto fibrous layer 32 where they are intermingled with the natural wood pulp fibers deposited thereon as ~ust described. The vertical location of baffle 65 determines the degree of crossover, or the relative proportions of short fibers 24 and longer fibers 25 that are deposited at each thickness level to form fibrous layer 23.
The resulting fibrous material made up of two components, first layer 23 and second layer 32, is carried to the right by endless belt 52 in Figure 7 for further treatment.
When fiber end portions 36 an~ 40 that extend outwardly beyond their respective boundary surfaces 38 and 42 penetrate the opposing fibrous layer as layers 23 and 32 are brought together in the first step of this invention, considerable contact is effected between fiber segments of synthetic wood pulp fibers in second layer 32 and ~ibers of first layer 23. The resulting interfiber contact--with fiber segments of synthetic wood pulp fibers 34 of second layer 32 resting in con-tact with first layer 23 after either free fiber ends 36 or 40~ or some of both, have inserted themselves F~ into interstices between the fibers of the other layer--,i Zl is illustra~ed in Figure 6 in diagrammatic ~ashion.
Figure 6 is not inte~ded to suggest that the precise types of contact zones shown there are necessarily identifiable in the product of this invention, but the contact zones shown are intended to suggest some considerable degree of contact between the fibers in question It may happen that some exposed fiber end portions 36a and 40a as shown in Figure 5 will move into contact with each other as seen in Figure 6 when ~ibrous layers 23 and 32 are brought together in the first step of the method of this invention. Contact zones of this type are indicated by the letter "a" in Figure 6 at several locations in the left-hand portion of the figure, and also in the right-hand portion.
In some cases, outwardly extending fiber end portions 36b and 40b may collide with each other as fibrous layers 23 and 32 are brought together, and be bent into positions where they maintain fiber contact.
Such fiber contact is indicated by the letter "b" in the left-hand portion, the middle, and the right-hand portion of Figure 6.
The interfiber contact thus far described is believed to provide the major portion of the structural integrity of the fibrous material. The contact described may in some instances be further supplemented by an actual "intermeshing" of exposed fiber end portions with one fiber end sliding behind another fiber end to pro-vide not only fiber contact but a more positive engage-3 ment somewhat similar to the mechanical interengagement or interentanglement of the bent fibers that is present throughout the body of fibrous layers 23 and 32. How-ever, it is believed that the incidence of such inter-meshing of fiber ends is typically not very high.
Another type of interfiber contact of less importance, but still adding to the structural integrity ~s~z;~

of the fibrous material, is the essentially two-dimensional contact of parallel fiber segments lying at the respective boundary surfaces 38 and 42 of fibrous layers 23 and 32 when they arebrought together. Examples 5 of this supplementary interfiber contact are shown at "c" at the left-hand side~ the middle, and the right-hand side of Figure 6.
Some exposed and protruding fiber end portions 36d and 40d fail to make contact with any fibers in the opposing fibrous layers. Examples of such situations are shown at the left-hand end, and at several places near the middle, of Figure 6.
In the second step of this method of this invention, heat is applied in the absence of pressure 15 at least to the portions of fibrous layers 23 and 32 in which synthetic wood pulp fibers 34 of layer 32 are in contact with fibers 24 and 25 of layer 23, to raise the temperature of fibers 34 to or a little above the melting point of the synthetic wood pulp fibers. In 20 other words, heat as described is applied at least to the fibrous regions in which contact zones, a, b, and c in Figure 6 are located. As a result, some or all of synthetic wood pulp fibers 34 that are in contact with fibers of first layer 23 are fused and bonded to the 25 'latter fibers.
As indicated, heat is applied during this second step at least to the portions of layers 23 and 32 that lie immediately adjacent interface 38/42 located between them. The remaining portions of the'fibrous material produced by-the method of this invention may, if'desired, also be subjected to heat in the absence of pressure, and this will be particularly useful if synthetic wood pulp fibers are distributed in other portions of the fibrous material in addition to those 35 immediately adjacent interface 38/42.
The right-hand portion of Figure 10 shows 2~

diagrammatically means for applying heat to fibrous layers 23 and 32. Heating means 66, which may be a dielectric heater, infra-red heater, radiant heater, or other heating means, applied heat to the two fibrous layers supported on endless belt 52, as they move to the right in Figure 10.
- Synthetic wood pulp fibers 3~ in second layer 32 should have a melting point lower than the melting point or degradation temperature of every other type of fibers contained in layers 23 and 32. Preferably, the melting point of the synthetic wood pulp fiber should be at least 10~ to 20C. lower than the melting point of the other fibers.
Additional bonding may be provided by deposit-ing adhesive binder on fibrous layers 23 and 32 from applicator means 67 shown diagrammatically in Figure 10.
Applicator means 67 is typically a source of binder coupled with a suction box. Alternatively, applicator means 67 may comprise spray apparatus for the application of binder in the form of droplets. The binder is prefer-ably distributed throughout both layers. After its introduction into the two layers, the adhesive binder is activated by drying and/or heating, which can be supplied by diagrammatically shown means 68.
In another method of this invention a first layer of compactly assembled, adhesive bonded, natural wood pulp fibers, such as a wet-laid web, is brought together with a second, and optionally, a third layer of loosely assembled fibers having a multiplicity of 3 interstices between them, such as an air-laid web, comprised of liquid absorbent natural wood pulp fibers and ~ettable synthetic wood pulp fibers of a lower melt-ing point than the other fibers of the two layers as indicated above.
In the second step of this method, conventional emboss laminating equipment is employed to apply heat ~5~32~

and pressure to the layers in a discontinuous embossing pattern across the layers. The combination of pressure and temperature applied to the synthetic wood pulp fibers softens them, and may in fact, melt them. The synthetic wood pulp fibers of the second, and optionally the third layer are thus heat fused and reliably bonded to the fibers of the backing layer of the device.
In the final step of this method, heat is applied in the absence of pressure to the rest of the second and third layers in the unembossed areas re-maining after the embossing pattern has bee~ imposed on the material. In this step, synthetic wood pulp fibers contained in the second and third layers are heat fused and bonded to each other and to other fibers in that layer. A three-dimensional network of stabilized absorbent cellulose fibers having good liquid holding capacity is thus provided in the portions of the second and third layers lying in the unembossed areas of the discontinuous pattern.
In yet another method of this invention, a plurality of irregularly arranged, intersecting, over-lapping, mechanically interengaged, loosely assembled fibers, including both natural wood pul-p fibers and synthetic wood pulp fibers, is brought together to posi-tion the two types of fibers in different proportions inthree different layers positioned parallel to the median plane of the material. Heat is then applied in the absence of pressure to the plurality of fibers thus arranged, to fuse and bond at least some of the synthetic 3 wood pulp fibers with other segments of fibers at a plurality of junctures throughout the ~ibrous material.
A fiber structure that is self-supporting in the absence of any additional binder is thus produced.
As indicated above, fibrous material 10 shown in Figure 9 may if desired be formed by ~eans of an air deposition process. Figure 11 provides a diagrammatic S~l drawing in side elevation of apparatus that may be used in this manner.
The left-hand portion of the apparatus in Figure 11 is similar to the~ web forming apparatus dis-closed in co~monly assigned~Patent Nos. 3,740,797 to Farrington, 3,768,118 to Ruffo et al, and 3,772,739 to ~ovgren. A board 50 of synthetic wood pulp fibers is fed into air deposition apparatus 52 between guide plate 54 and feed roll 56, into edgewise contact with lickerin 58, which separates the web into individual fibers of synthetic wood pulp. At the same time, a board 60 of natural wood pulp fibers is fed into air deposition apparatus 52 between guide plate 62 and feed roll 64, into edgewise contact with lickerin 66, which separates the web into individual fibers of natural wood pulp.
As synthetic wood pulp fibers and natural wood pulp fibers are directed downward from lickerins 58 and 66, respectively, they are intermingled to form fibrous material 10, which moves from left to right with the endless belt in Figure 11. Air deposition apparatus 52 can be adjusted, as explained in the patents referred to above which disclose such apparatus, to produce different proportions of synthetic ~ood pulp fibers and other fibers in the various regions of the resulting nonwoven fibrous material at or parallel to the median plane of the material.
For additional fabric strength, if desired, adhesive binder in latex form may be sprayed on the exposed boundary surface portions 18 of region 12 of the resulting fibrous material 10. If added, the binder should be applied in an amount equivalent to about 1~
by dry weight of the resulting fibrous material. Any suitable binder employed with nonwoven fibrous materials may be used. Binder applying means 70 is shown diagrammatically in Figure 11, and drying means 72, such as a dielectric heater, infra-red heater, radiant heater, ~s~z~

or other heating means, is shown diagrammatically at 72.
As a subsequent step in the method of this invention, exposed boundary surface 18 of region 12 of fibrous material lO can be lightly calendered to partially smooth the boundary surface. Calendering means 74 is shown diagrammatically in ~igure ll.
The product resulting from use of the method described is a high loft, low density, nonwoven fibrous material having good wet strength, softness, abrasion resistance, and good liquid absorbency and liquid reten-tion.
The above detailed description is given for clearness of understanding only. No unnecessary limita-tions should be understood therefrom,`as modifications will be obvious to those skilled in the art.

Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A high loft, low density, nonwoven fibrous material of good stability and mechanical integrity, and good hand and softness, which comprises a first layer of irregularly arranged, intersecting, overlapping, mechani-cally interengaged fibers, said fibers including fibers other than thermoplastic synthetic wood pulp fibers, and a second layer of loosely assembled fibers defining interstices therebetween, in contact with said first layer at an interface therebetween, said second layer including, in addition to other types of fibers present, thermoplastic synthetic wood pulp fibers located at least in portions of said second layer adjacent said interface between said two layers, segments of at least some of the thermo-plastic synthetic wood pulp fibers in said second layer being in contact with and heat fused with segments of fibers of said first layer, said thermoplastic synthetic wood pulp fibers in the second layer having a melting point lower than the melting point or degradation temperature of every other type of fibers contained in said two layers.

2. A multi-ply fibrous material suitable for use as a wipe, swab, sponge or other cleaning device which comprises the high loft, low density, fibrous material of Claim 1, said fibers in said first layer comprising compactly assembled natural wood pulp fibers bonded to each other with an adhesive binder to provide good wet strength, and said other types of fibers in said second layer are natural wood pulp fibers, said thermo-plastic synthetic wood pulp fibers in said second layer being wettable, segments of a portion of the thermoplastic synthetic wood pulp fibers of said second layer being heat fused and bonded to said first layer in a discon-tinuous pattern of embossed areas alternating with unembossed areas across said first layer to provide a reliable bond between said layers, the remainder of said thermoplastic synthetic wood pulp fibers being heat fused and bonded to each other and to other fibers in said second fibrous layer to provide a. three-dimensional network of stabilized absorbent cellulose fibers having good liquid holding capacity in the portions of said second fibrous layer lying in the unembossed areas of said discontinuous pattern.

3. A multi-ply fibrous material as in Claim 2, which further comprises a. third layer of fibers similar to said second layer, said third layer in contact with said first layer at an interface therebetween, segments of a portion of the thermoplastic synthetic wood pulp fibers in said third layer being heat fused and bonded to said first layer in said discontinuous pattern of embossed areas alternating with unembossed areas to provide a. reliable bond between said first layer and said third layer, the remainder of said thermoplastic synthetic wood pulp fibers in said third layer being heat fused and bonded to each and to other fibers in said third layer to provide a three-dimensional network of stabilized absorbent cellulose fibers having good liquid holding capacity in the portions of said third fibrous layer lying in the unembossed areas of said discontinuous pattern.

4. A high loft, low density, nonwoven fibrous material as in Claim 1, having excellent resistance to delamination wherein said second layer is in firm engage-ment with said first layer at the interface thereof, said fibers in said first layer being loosely assembled defining interstices therebetween and said thermoplastic synthetic wood pulp fibers being present in said second layer in the portions of said layer at the interface between the two layers in a. quantity sufficient to occupy at least about 10% of the area occupied by fiber segments contained in said second layer at said interface, fibers of at least one of said two layers extending across the interface between the two layers with free end portions of said fibers positioned within interstices between fibers in the other of said layers, at least some of the interstices between fibers of said first layer being of a width at least twice as large as the mean diameter of said synthetic wood pulp fibers in said second layer, at least some of the interstices between fibers of said second layer being of a width at least twice as large as the mean diameter of the fibers in said first layer.

5. A fibrous two-ply facing material for an absorbent product such as a diaper, comprising the high loft, low density, nonwoven fibrous material of Claim 1, said fibers in said first layer being loosely assembled defining interstices therebetween and comprising natural wood pulp fibers, said other types of fibers in said second layer including natural wood pulp fibers intermixed with said thermoplastic synthetic wood pulp fibers in said second layer, said thermoplastic synthetic wood pulp fibers being present in the portions of said second layer at the interface between the two layers in a quantity sufficient to occupy no more than about 6% of the area occupied by exposed fiber segments contained in said first layer at said interface, thermoplastic synthetic wood pulp fibers in said second layer being in contact with and heat fused with other fibers in said layer to form a fiber structure of sufficient wet strength and integrity to be self-supporting in both dry and wet condition without any additional binder, fibers of at least one of said two layers extending across the inter-face between the two layers with free end portions of said fibers positioned within interstices between fibers in the other of said layers, at least some of the interstices be-tween fibers of said first layer being of a width at least twice as large as the mean diameter of said synthetic wood pulp fibers in said second layer, at least some of the interstices between fibers of said second layer being of a width at least twice as large as the mean diameter of the fibers in said first layer, fibers in each of said first and second layers being bonded with one another and with fibers in the other layer by a water soluble adhesive binder to provide sufficient mechanical integrity throughout said two-ply facing material to allow normal handling of the dry material as a whole, and to help provide, together with the already existing mechanical interengagement of whole fibers in said first layer, sufficient mechanical integrity in said first layer to avoid disintegration of said first layer when the bond between said two layers is weakened by dissolving out only a portion of said water soluble binder and is then ruptured by pulling said two layers apart, so that the dry, unsoiled two-ply facing material can be subjected to normal handling without damage to the material, and after use the facing material and any solid waste matter deposited thereon can be immersed in water for a time, swirled around in the water to dissolve out only a portion of said water soluble binder, and pulled apart into two layers as above described, to produce self-supporting, second layer to be discarded separately from the first layer, and a separate assemblage of substantially all said natural wood pulp fibers that were originally in said first layer, which assemblage of fibers together with any residue of said solid waste matter not rinsed away by said swirling action can be flushed down a waste disposal system, where after the dissolving out of said water soluble binder is completed the assemblage will disintegrate into a multiplicity of separate individual fibers or small clumps of fibers.

6. A nonwoven fibrous material having good wet strength, softness, abrasion resistance, and liquid absor-bency and retention which comprises the high loft, low density, nonwoven fibrous material of Claim 1, said fibers in said first layer and said second layer include both natural wood pulp fibers and thermoplastic synthetic wood pulp fibers, said fibers in said first layer being loosely assembled defining interstices therebetween, and said material further comprising a third layer of similarly disposed natural wood pulp fibers and thermoplastic synthetic wood pulp fibers, said thermoplastic synthetic wood pulp fibers being present in said first layer in an amount from about 6% to about 30% by weight of the fibers, said thermoplastic synthetic wood pulp fibers being present in said second layer in a smaller proportion than the pro-portion of synthetic wood pulp fibers in said first layer, and said synthetic wood pulp fibers being present in said third layer in a proportion greater than the proportion of synthetic wood pulp fibers in said second region but less than the proportion of synthetic wood pulp fibers in said first region, said first and third regions being located on opposite sides of said second region, segments of said synthetic wood pulp fibers being heat fused with other segments of synthetic wood pulp fibers and with segments of other fibers at a plurality of junctures throughout said fibrous material to form a self-supporting fibrous structure which does not require any additional binder.

7. In a diaper structure comprising a facing layer, an absorbent batt and an impervious backing layer in which said facing layer and said backing sheet are outermost layers and said batt is positioned between said facing layer and said backing sheet, the improvement wherein said facing layer comprises the high loft, low density, nonwoven fibrous material of Claim 1.

8. A method of producing a high loft, low density, nonwoven fibrous material having thermoplastic synthetic wood pulp fibers in at least one region of said material parallel to or including its median plane which comprises:
bringing together a first layer of irregularly arranged, intersecting, overlapping, mechanically interengaged, fibers defining interstices therebetween, said fibers in-cluding fibers other than thermoplastic synthetic wood pulp fibers, said layer of fibers having free fiber ends extend-ing outwardly from at least one boundary surface of the layer, with a second layer of similarly disposed fibers, said second layer including, in addition to other types of fibers present, thermoplastic synthetic wood pulp fibers located at least in surface portions of said layer immediately adjacent said one boundary surface of the first layer, to bring at least some of the fiber segments of thermoplastic synthetic wood pulp fibers or said second layer into contact with said first layer by inserting free fiber ends from at least one of said layers into interstices between fibers in the other of said layers, said thermo-plastic synthetic wood pulp fibers in the second layer having a melting point lower than the melting point or degradation temperature of every other type of fibers con-tained in said two layers; and applying heat in the absence of pressure at least to the portions of said two fibrous layers in which thermo-plastic synthetic wood pulp fibers of said second layer that are in contact with fibers of said first layer are located, to fuse and bond at least some of said contacting thermoplastic synthetic wood pulp fibers to fibers of said first layer and thereby produce a fibrous material of good stability and mechanical integrity, as well as good hand and softness.

9. A method of producing a high loft, low density, fibrous material which displays excellent resistance to delamination comprising the method of Claim 8 wherein said first and second layers comprise loosely assembled fibers, at least some of the interstices between fibers of said first layer being of a width at least twice as large as the mean diameter of said thermoplastic synthetic wood pulp fibers in said second layer, at least some of the interstices between fibers of said second layer being of a width at least twice as large as the mean diameter of the fibers in said first layer, said thermoplastic synthetic wood pulp fibers at the boundary surface of said second layer adjacent said first layer being present in a quantity sufficient to occupy at least about 10% of the area occupied by exposed fiber segments contained in said second layer at its boundary surface.

10. A method of producing a fibrous two-ply facing material for an absorbent product such as a diaper which comprises:
the method of Claim 8, wherein said first and second layers comprise loosely assembled fibers, at least some of the interstices between fibers of said first layer being of a width at least twice as large as the mean diameter of said thermoplastic synthetic wood pulp fibers in said second layer, at least some of the interstices between fibers of said second layer being of a width at least twice as large as the mean diameter of the fibers in said first layer, and wherein the fibers of said first layer include natural wood pulp fibers, and the other types of fibers of said second layer include natural wood pulp fibers which are intermixed with said synthetic wood pulp fibers in said second layers, said synthetic wood pulp fibers being present at the boundary surface of said second layer adjacent said first layer in a quantity sufficient to occupy no more than about 6% of the area occupied by exposed fiber segments contained in said second layer at its boundary surface, and further comprising the steps of:
applying heat in the absence of pressure to said two fibrous layers thus brought together, to fuse at least some of said synthetic wood pulp fibers to each other and to some of said other fibers within said second layer to form a self-supporting fibrous structure in said second layer;
introducing a water soluble adhesive binder into said two fibrous layers and at the interface where said two layers have been brought together as described, drying and curing said binder to produce a facing material with sufficient mechanical integrity to allow normal handling of said facing material, and in addition help provide, together with the already existing mechanical engagement of whole fibers in said first layer, sufficient mechanical integrity in said first layer to prevent its disintegration when the bond between said two layers is ruptured to produce delamination of the two layers after only a portion of said water soluble adhesive binder has been dissolved out of the facing material and delaminating forces have been applied to the two layers.

11. A method of producing a multi-ply fibrous material suitable for use as a wipe, swab, sponge or other cleaning device which comprises:
bringing together a first backing layer of irregularly arranged, intersecting, overlapping, mechanically interengaged, compactly assembled natural wood pulp fibers bonded to each other with adhesive binder to provide wet strength, with at least one liquid absorbent layer formed of irregularly arranged, intersecting, overlapping, mechanically interengaged, loosely assembled fibers having a multiplicity of interstices between them, said fibers including both liquid absorbent natural wood pulp fibers and wettable thermoplastic synthetic wood pulp fibers, said thermoplastic synthetic wood pulp fibers in said second-named fibrous layer having a melting point lower than the other fibers of that layer and of said first layer, applying heat and pressure to said layers in a discontinuous embossing pattern across said layers to heat fuse and reliably bond thermoplastic synthetic wood pulp fibers of said second-named layer to said backing layer; and applying heat in the absence of pressure to the remainder of said juxtaposed layers to heat fuse and bond thermoplastic synthetic wood pulp fibers contained in said second-named fibrous layer to each other and to other fibers in said second-named layer to provide a three-dimensional network of stabilized absorbent cellulose fibers having good liquid holding capacity in the portions of said second-named fibrous layer lying in the unembossed areas of said discontinuous pattern.

12. A method of producing a high loft, low density, nonwoven fibrous material having good wet strength, softness, abrasion resistance, and liquid absorbency and retention which comprises:
bringing together a plurality of irregularly arranged, intersecting, overlapping, mechanically inter-engaged, loosely assembled fibers including both natural wood pulp fibers and synthetic wood pulp fibers to position said two types of fibers in different proportions in various layers parallel to the median plane of the material, with synthetic wood pulp fibers being positioned in a first layer in an amount from about 6 per cent to about 30 per cent by weight of the fibers, in a second layer in a smaller proportion than in said first layer, and in a third layer in a proportion greater than in said second layer but less than in said first layer, said first and third layers being located on opposite sides of said second layer, the melting point of said synthetic wood pulp fibers being lower than the melting point of all other fibers in said fibrous material, and applying heat in the absence of pressure to said plurality of fibers thus arranged to fuse and bond at least some of said synthetic wood pulp fibers with other segments of synthetic wood pulp fibers and with segments of other fibers at a plurality of junctures throughout said fibrous material to form a self-supporting fiber structure which does not require any additional binder.